The moniker Gemini Twins was never used while they were active, it wasn't until Murder Machine was published that, that name was used in reference to them. From what I understand, Joseph Testa has numerous siblings and a large family in New York and Anthony Senter is going to Vegas with his wife.
Harvey "Chris" Rosenberg was introduced to Roy DeMeo by longtime gangland associate Danny Grillo in 1966, after Roy began recruiting talent for his burgeoning auto theft operation. Chris brought in Senter and Testa whom he knew from the neighborhood but lived in a different part of Canarsie. The actual ambush of the Cuban drug dealers was at Senter's basement, a few houses down from Testa's and behind Henry Borelli's home. Nino instructed Roy DeMeo to whack Rosenberg which he did shooting him in the head, dropping him to one knee. Senter then putting several bullets behind Rosenberg's ear. Rosenberg's body was placed in his car, machine gunned, and left the center divider on Flatbush Ave, just before Marine Parkway and Marine Park Bridge.
I think Roy DeMeo was murdered at Patty Testa's auto shop by Nino Gaggi, Testa, Senter, and possibly Henry Borelli, according to FBI agent Art Ruffles. In Murder Machine, Roy left his personal effects at home, indicating knowledge of what was waiting for him, when he was summoned to the sit down. Testa and Senter were required to put a bullet in Roy's head to ceremoniously end their business with him and start fresh with the Lucheese's under Frank Lastorino. Lastorino had a business around the corner from Patty Testa's auto shop and was suspected of murdering Patty Testa on orders from Gaspipe Casso years later. None of Roy's rackets were absorbed by the Lucchese's. The Empire Blvd auto theft operation was blown up by the Feds after vehicles with faked VIN number plates were discovered at the port of Newark and his loanshark book was kept by Albert. Roy had a huge port and sex trade operation in Times Square, where he had an office on the eigth floor of Sex World, he shared with porn mogul Richard Basciano.